1. Field of the Invention
This invention relates generally to downhole obstacle sensing and data communication systems for guided boring and drilling apparatus, and more particularly to a downhole buried utility sensing and data transmission system having sensors capable of detecting the existence of various different types of buried utilities and objects and making calculations as to the radial separation distance between the detected utilities and the drill head and transmitting data between the down hole drill head to the surface.
2. Brief Description of the Prior Art
Since its inception into the underground utility construction industry, guided boring technology has experienced rapid advances and evolution in the types of systems available and the diameters, distances and accuracies to which underground utilities can be installed. Guided boring requires the capability to control hole direction and monitor its position in space. Currently, most guided boring systems utilize "pipe locators" to track the physical location and orientation of the boring head. These "pipe locators" consist of a small active transmitter placed in or near the drill head and a pair of highly tuned receiver coils. The devices are low cost and provide reasonably accurate data. There main limitations are the need for surface access along the route of the bore to take readings and their relatively shallow depth capability.
Solid-state compasses known as "steering tools" are also used for tracking and guidance of boring tools when economics and work conditions allow. These steering tools are significantly more expensive than "pipe locators" and require an insulated wire connecting the down hole instrumentation to the surface.
More recently, wireless systems, referred to generically as "Measurement-While-Drilling" (MWD) systems have been developed. The MWD systems provide wellbore directional data without requiring an insulated hard wire link to bring information to the surface. The wireless MWD systems provide improved reliability, simpler operation, higher speed, greater directional control and longer distances and they accommodate a greater range of hole sizes.
In spite of the industry's advances in guidance technology, there is no method of employing sensors down hole to detect the presence of buried utilities in the immediate vicinity of the drill head and communicate this information to the surface utilizing the "pipe locator", steering tool or MWD directional guidance platforms. Rather, the present state of the art is to dig test holes to physically confirm the exact location of other buried utilities or to employ "one call" location services which use walkover line tracing technologies to locate the approximate position of energized power cables or telecommunications lines on which has been imposed a fixed frequency signal. The problems with these systems are the requirement for surface access, which may impose safety risks in the case of highway crossings, or is impractical in the case of river crossings which support a lot of shipping activity. In addition, current devices do not operate in real time and therefore are of little use if the actual drill path varies from the path previously scanned for utilities. Finally, the devices do not provide accurate calculation of physical location which increases the likelihood of inadvertent strike.
McDonald et al, U.S. Pat. No. 5,467,083, which patent is hereby incorporated herein in its entirety by reference, discloses a wireless downhole electromagnetic data transmission system that impresses a digitally encoded message upon the drill string using frequency shift keying of the electromagnetic waves. The transmitted message is picked off at the surface by a signal receiver-demodulator unit and gravity and magnetic field vectors are combined with the hole length to calculate x, y, and z hole coordinates and derive hole position vectors and the presence of energized AC and DC power cables in the immediate vicinity of the boring head. The present invention is a significant improvement over this patent in that with the present system, the sensors respond to stimuli based on the materials used to construct the utility lines (pipes and cables) or from the energy associated with transmission of the particular utility service and the demodulated message provides specific information related to the particular different types of buried utilities detected, the level of alarm and the distance between the drill head and the obstacles. The present system may be used with an electromagnetic data transmission system such as that described in U.S. Pat. No. 5,467,083, an RF system such as used with locator sondes, or other suitable systems using well known encoding protocols for steering the tool and transmitting the information to the control point, for example; phase shift keying, pulse width modulation, amplitude modulation or frequency shift keying. The data can also be communicated using a direct wire line link which transmits analog or digitally encoded data.
The present invention is distinguished over prior art in general by a downhole buried utility sensing and data transmission system disposed at the lower end of a drill string and having sensors capable of detecting the existence of various different types of buried utilities and objects and making calculations as to the radial separation distance between the detected utilities and the drill head and transmitting data between the down hole drill head to the surface. The sensors respond to material properties used to construct the utility lines or the energy fields created by the operation of these lines (pipes and cables) or from the energy associated with transmission of the particular utility service, including sound energy resulting from fluid flow and electromagnetic energy from electric currents. The system can detect and distinguish the presence of ferromagnetic metallic objects including steel pipes and structures; non-metallic utility infrastructure including gas pipelines, concrete sewer lines, telecommunication lines, and cable systems outfitted with RF tracer lines and transmitters; energized AC and DC power cable systems; and determining the approximate range, relative azimuth, and elevation of the sensors relative to the detected utility or object. The system also supports automatic cessation of drilling operations by combining the warning information with microprocessor control of drill string rotation and thrust.